Rock Mechanics Quiz 3 Flashcards
Define Rock slopes.
Rock slopes either occur naturally or are engineered by people as products of excavations to create space for buildings, highways and railway tracks, powerhouses, dams and mine pits.
What is the main purpose of slope stability analysis?
In most civil and mining engineering projects, the main purpose of slope stability analysis is to contribute to the safe and economic design of rock slopes.
Define plane failure and illustrate it.
Sliding without rotation
along a face; single or
multiple blocks
Define Wedge failure and illustrate it.
Sliding without rotation on two nonparallel
planes, parallel to their line of intersection;
single or multiple blocks
Define Circular failure and illustrate it.
Sliding on a cylindrical
face
Define Toppling failure and illustrate it.
Forward rotation about
an edge/base; single or
multiple blocks
Describe a large rock slope and single sliding mass in relation to mode of failure.
If a rock slope is large and embraces a mix of rock types and structures, more than one of the basic failure modes may be
expected. On the contrary, within a single sliding mass, it is not unreasonable to find more than one of the basic failure modes at the site.
Discuss stability of rock slopes.
The stability of rock slopes is greatly controlled by the shear strength along the joints and interfaces between the unstable rock block/wedge and intact rock, as well as by the geometric interaction of jointing and bedding patterns in the rock mass constituting the slope.
Challenges in determining the magnitude of the available shear strength.
The magnitude of the available shear strength along joints and interfaces is very difficult to determine due to the inherent variability of the material and the difficulties associated with sampling and laboratory testing.
Enumerate the factors that directly or indirectly influence the
strength along the joints.
- The planarity and smoothness of the joint’s surfaces. A smooth planar surface will have a lower strength than an irregular and rough surface.
- The inclination of the discontinuity plane with respect to the slope.
- The openness of the discontinuity, which can range from a small fissure to a readily visible joint
- The extent of the weathering along the surfaces and the possible infill of the joint with weaker material such as clays and calcareous materials. A calcareous infill may potentially increase the strength of the joint, whereas a soft clay infill may reduce the strength of the joint to
the same level as the clay material itself.
What are calcareous materials?
Calcareous Materials are compounds of calcium and magnesium.
Define piezometer.
Piezometer is used to measure underground water pressure. It converts water pressure to a frequency signal via a diaphragm and a tensioned steel wire.
Role of Limit equilibrium methods in slope stability analysis.
Limit equilibrium methods have been useful in developing the fundamental understanding of rock slope stability analysis
for simple modes of failure.
Role of Numerical methods in slope stability analysis.
Numerical methods help analyze the rock slopes, especially failing in a combination of basic modes and other known failure modes such as erosion, slumping, block torsion, and etc.
Define factor of safety (FS) against sliding of a rock block
Factor of Safety (FS) against sliding
of a rock block is defined as FS=Fr/Fi where Fr is the total force available to resist the sliding of rock block and the Fi is the total force tending to induce sliding.
Discuss limiting equilibrium and stable slopes.
For a slope on the point
of failure, a condition of limiting equilibrium exists in which Fr = Fi, and thus FS = 1. For stable slopes, Fr > Fi, and therefore FS > 1. In practice, rock slopes with FS = 1.3 to 1.5 are considered to be stable.
Define angle of internal friction.
angle of internal friction is the slope of a linear representation of the shear strength of earth materials.